Dynamic bearings, as has been alluded to previously, are generally formed between a rotatable member and another member, the two members having juxtaposed surfaces between which a dynamic film or layer of a fluid is induced to form as an antifriction medium.
Specifically, such dynamic bearings can be used in high-speed expansion turbines and while the fluid-antifriction medium can be a gas, it frequently is a lubricating oil.
To induce the flow of the medium into the interfacial region and to maintain the dynamic cushion of this fluid within the region, at least one of the surfaces, usually that of the rotatable member, is provided with a groove/rib pattern designed to induce the flow of the medium into the interfacial region and generate the dynamic layer referred to previously.
When the two surfaces are to define an axial bearing, the pattern is one of spiral grooves separated by corresponding ribs or lands between the grooves.
For radial bearings, i.e. when the surfaces are juxtaposed cylindrical surfaces, the groove pattern is a herringbone or generally fishbone pattern, i.e. the grooves or ribs have a chevron configuration.
The grooves which are separated by the ribs or lands, can have a depth of up to 100 micrometers.
For producing these groove and land patterns, various techniques have been developed. For example, mechanical machining techniques have been used, as well as such nonmechanical techniques as purely chemical etching and high-energy techniques such as ion-beam machining. All of the earlier techniques which have been developed for the purpose have been found to have various disadvantages and we may mention, for example, that etching results in inaccurate and rough groove edges, rounded contours of the ribs or lands between the grooves, and other detrimental characteristics such as rough groove bases and flanks and nonuniform groove depths.
All of these may give rise to nonuniform operation unless expensive after-machining techniques are employed.
For completely different purposes, namely the generation of perfectly flat surfaces free from grooves and the like, electropolishing has been developed (see Metalloberflaeche 38, 1984, page 505 to 511). Electropolishing, also known as electrochemical polishing has been used, for example, to generate smooth surfaces in metallography and microphotography following grinding, and for the decorative polishing and shining of nonferrous metals. Indeed, as far as we are aware, electrochemical polishing has only been employed on an industrial or chemical level for the smoothing or polishing of high-value plane metal surfaces in which the last thing that was desired was any form of cavity, groove or the like.